1. Field of the Invention
This invention relates to the damping or detenting of stepper motors in general and, more particularly, to a detenting technique which achieves a velocity controlled detent without the need of a tachometer by utilization of variable reluctance feedback transducers which are rotationally positioned on the motor such that the velocity feedback of each phase is in phase with the torque output of its respective phase. Control is based on the output of the velocity feedback of the transducers.
2. Description of the Prior Art
Accurate control of stepper motor positioning in many modern day applications is required. Most systems control stepper motors such that accurate control of the velocity profile is maintained through acceleration, steady state travel and deceleration. The motors, following the deceleration period, are detented at the desired location.
In the prior art most systems are devoted to the control of stepper motors over a period of a number of steps to position the motor from an initial location to a desired location. This gross control of the motor is intended to cause the load to be moved as rapidly as possible from a starting position to a desired position. These systems in the prior art, once the stepper motor has arrived at the approximate desired position, rely on the inherent detenting of the stepper motor for final detenting. Alternately, electrochemical detents can be used.
U.S. Pat. No. 3,399,753 entitled "Printer with Type Wheel Rotatable in Either Direction" to Revelie, filed Jan. 10, 1966, issued Sept. 3, 1968 is a patent which is directed toward a technique for moving a print wheel which is driven by a stepper motor in the shortest direction. There is no concern in the patent with the problem of capture or detent oscillation. This problem is occasioned by the fact that at the home or desired position there is zero torque in the motor and due to the kinetic energy in the load, overshoot and consequently oscillation occurs. Instead, the patent is directed toward moving in the quickest possible manner to the desired position.
U.S. Pat. No. 3,663,880 entitled "Apparatus for Controlling the Relative Position Between Two Relatively Movable Members," to Gabor, filed Sept. 14, 1970, issued May 16, 1972 is an example of a prior art stepper motor control system. This system teaches the control of the movement of a load under control of a stepper motor for a large distance. As shown in FIG. 2C of the patent, the velocity is controlled for an acceleration period, a steady state period, a deceleration period, and a homing or detenting period. The overall structure of this system is designed for rapidly moving a load from one point to another. There is no teaching in this system of the problems associated at the home position with motor overshoot.
U.S. Pat. No. 3,789,971 entitled "Servo Control System for a Serial Printer Print Head" to Deyesso, filed June 21, 1971, issued Feb. 5, 1974 is another prior art system which teaches the control of a stepper motor for movement of a load over a large distance. In this system the load is moved in the closest direction at multiple load velocities to cause rapid positioning. Again, there is no concern in this system with detent oscillation or capture at the final position.
U.S. Pat. No. 3,954,163 entitled "High Speed Printer With Intermittent Print Wheel and Carriage Movement" to Gabor, filed Sept. 11, 1974, issued May 4, 1976 is another prior art system which is concerned with the movement of a load over a large distance as rapidly as possible. This system is quite similar to the afore discussed U.S. Pat. No. 3,663,880 in that they employ the same concept for control. Again, there is no concern in this patent with detent oscillation or capture occasioned by the kinetic energy of the load at the zero torque or detent position.